This invention relates to a system for supplying hot water such as might be used for potable systems and heating in dwellings.
Great interest has developed recently in the area of conservation of energy and utilization of alternate energy sources. Among the sources recently receiving attention is solar energy. Goethermal energy and waste heat energy are also being investigated. In utilizing such energy sources, attention must be directed to maximizing system efficiency and minimizing the initial investment in order that such systems may be considered economically competitive with more conventional means for space heating and potable water heating.
Systems have been developed which employ conventional solar panels for collecting solar heat. This accumulated solar heat has then been stored to augment conventional water heating or space heating. In such systems, it is common to run the heating fluid through the panels when the panels are hotter than the storage area. The storage area is in turn coupled with, for example, a water heater as the supply source therefor. The water already retained within the water heater is generally kept warm by more conventional energy sources such as gas or electricity.
Systems for maximizing the efficiency of more conventional heating sources have also been developed. One advanced means for improving the overall energy use in a dwelling or other structure has been developed by the present inventor. This system includes a circuit for constantly circulating hot water through a residence, group of residences or other structures. This circulating hot water may be employed as an almost immediate source of hot water to fixtures and through radiators for space heating. Through proper design, energy efficiency can be achieved. This continuous loop hot water system has been the subject of a number of patents and applications, the disclosures of all of which are incorporated herein by reference. A heating system is disclosed in Piper U.S. Pat. No. 3,526,361. Another related heating system is disclosed in Piper U.S. Pat. No. 3,655,127. Further improvements on these systems are also disclosed in Piper U.S. Pat. application Ser. No. 289,401 now U.S. Pat. No. 4,576,333 concurrently herewith. Detailed patents regarding mounting of equipment and the like for such systems include Piper U.S. Pat. No. 3,926,537.
Both the continuous loop hot water system and the type of systems employing solar energy panels or other heat sources which may not be available on a continuous basis have heretofore employed maintenance heating by a conventional water heating mechanism. In the case of conventional water heating for residences, the solar augmented system attempts to provide heated feed water to the water heater. The water heater must then elevate or maintain that heat by repeatedly starting up. This requirement has also been true of the continuous loop type system. Thus, efficiency is lost in the maintenance of the appropriate temperature level of water previously drawn into the system.
Looking in more detail to the actual features of solar energy systems, certain difficulties have been experienced in the operation of such systems. The first difficulty is experienced in the colder climate where such systems may experience the greatest economic utility. In such colder areas, problems with freezing of the water within the solar panels can develop during dark hours. When the water within the panels freezes, it expands to rupture the tubes of the system if some accommodation is not provided. A common method is to drain the panels during periods of extreme cold. This is less than advantageous in a potable water system and it also requires additional pumping capability to recharge the panels.
Another difficulty experienced by such solar systems is thermal cycling of the fluid within the system. During cold periods, the cooling of the panels results in a cooling of the water within the panels. This cooled water becomes comparatively heavier and tends to flow back from the panel thereby drawing warm water up into the panel. The warm water then cools and a continuous current is formed. Cycling thereby cools the entire mass of stored fluid resulting in a loss of heat energy. Even though this flow is sufficient to result in noticeable loss of efficiency, the flow may be small enough that conventional check valve arrangements are not activated by this termal cycling.
Thus, the emerging solar energy industry has been faced with mechanical difficulties in meeting the requirements of the environment and with efficiency difficulties in meeting the economic competition of more conventional systems.